FIELD OF THE INVENTION
The invention relates to a method for cooling the low-pressure turbine section of a steam turbine connected in a water/steam circuit, in which a coolant flows through the low-pressure turbine section, in particular during idling operation. The invention also relates to a device for carrying out the method.
A turbo set having a heating steam turbine in many cases is constructed in such a way that, when heat is extracted from an intermediate-pressure turbine section, a low-pressure turbine section or each low-pressure turbine section receives no substantial steam supply and therefore works in idling operation. However, that leads to increased heating of the blading in the low-pressure turbine section of the heating steam turbine, in particular in the case of a full heat extraction and a shut-off low-pressure turbine section.
It is known from German Published, Non-Prosecuted Patent Application DE 41 29 518 A1, corresponding to U.S. Pat. No. 5,490,386, to feed cooling steam and/or condensate to the low-pressure turbine section through a tap provided on the turbine in order to avoid inadmissible warming-up effects through ventilation losses in the blading. However, that involves a relatively large heat loss, since the heat contained in the cooling steam together with the lost heat resulting essentially from the ventilation is dissipated through the condenser connected downstream of the steam turbine and is therefore not available for heating purposes. Since an appropriately large quantity of the cooling steam for reducing a temperature rise in the blading resulting from the ventilation has to be selected, the heat losses are relatively high.